Tysinor is an orally administered systemic prodrug of 5′-deoxy-5-fluorouridine (5′-DFUR) which is converted to 5-fluorouracil. It works as a thymidylate synthase inhibitor. Thymidylate is the necessary precursor of thymidine triphosphate, which is essential for the synthesis of DNA, so that a deficiency of this compound can inhibit cell division. Nuclear transcriptional enzymes can mistakenly incorporate FuTP in place of uridine triphosphate (uTP) during the synthesis of RNA. This metabolic error can interfere with RNA processing and protein synthesis.